1. Field of the Invention
The present invention relates to a wire dot printer head provided in a wire dot printer and more particularly to a wire dot printer head having armatures with printing wires connected to the armatures respectively, the armatures being each adapted to pivot about a pivot shaft and between a printing position and a stand-by position.
2. Description of the Background Art
Heretofore there has been known a wire dot printer head wherein an armature with printing wire connected thereto is moved pivotally between a printing position and a stand-by position and a tip of the wire is caused to strike against printing paper when the armature is pivoted to the printing position, to effect printing.
In such a wire dot printer head it is necessary that the tip position of the wire be kept constant when the armature pivots to the printing position, thereby maintaining the printing pressure constant. To meet this requirement it has been proposed to provide a pivot shaft in the armature, allowing the armature to pivot stably about the pivot shaft.
In this case it is necessary that the pivot shaft be supported in a positionally fixed state by some suitable means. An example of a method for supporting the pivot shaft is pinching the pivot shaft between two opposed support members from both sides in the pivoting direction of the armature. In case of thus pinching the pivot shaft between two opposed support members, the pivot shaft comes into linear contact with the two support members.
Once the pivot shaft is pinched in linear contact with the two support members, a strong force is concentrated on the linear contact portions between the support members and the pivot shaft as the armature moves pivotally in printing, so that wear is apt to occur in the linear contact portions of the pivot shaft or the support members and the wear causes wobbling of the support shaft.
Once there occurs wobbling of the pivot shaft in printing due to such wear of the pivot shaft or the support members, there occur variations in the wire tip position during printing and there also occur variations in printing pressure, with consequent deterioration of the print quality.
Moreover, if wear dust resulting from the wear adheres to the armature, the pivotal motion of the armature may be obstructed.
Further, upon wobbling of the pivot shaft, the opposition area between members which constitute magnetic circuits for pivoting the armature varies, and when the opposition area becomes small, there increases a magnetic resistance, causing deterioration of the armature pivoting performance.
Accordingly, it is an object of the present invention to prevent the occurrence of wear of a pivot shaft serving as a fulcrum of an armature or wear of support members which pinch and support the pivot shaft and further prevent the occurrence of various inconveniences caused by wear of the pivot shaft or support members such as variations in printing pressure and consequent deterioration of the print quality, obstruction of a pivotal motion of the armature caused by the adhesion of resulting wear dust to the armature, and an increase of a magnetic resistance between members which constitute magnetic circuits and consequent obstruction of a pivotal motion of the armature.
The above object of the present invention is achieved by a novel wire dot printer head of the present invention.
According to the novel wire dot printer head of the present invention, a support groove having a concave shape is formed in at least one of support members which pinch and support a pivot shaft of an armature, and an outer periphery surface of the armature pivot shaft is allowed to get into the support groove in a state of surface contact with the groove, to increase the area of contact between the pivot shaft and the support members and prevent a local concentration of a strong force on the contact portions of the pivot shaft or the support members, thereby diminishing wear of the contact portions of the pivot shaft or the support members.